The present invention relates generally to combustion equipment, and more particularly to a flow control device for a combustor.
Gas turbine engines utilized in civilian and military aircraft typically adhere to emission and pollution standards. Reduction of such emissions, for example, is typically accomplished throughout the flight of the aircraft inclusive of take-off, climb, cruise and descent wherein it is desirable to optimize the burning of a fuel and an oxidizer (typically air) within a combustion chamber under all the abovementioned operating conditions.
The flow of air and the flow of fuel into the primary combustion zone of the combustion chamber vary greatly as a function of engine rotational speed and fuel feed conditions. The disparities in air-fuel richness are great between low and full power operating modes of the engine. During low power operation, the air-fuel mixture is lean and the engine typically emits a large amount of carbon dioxide in some designs. During this operational phase, air flow, pressure, temperature and air-fuel richness are comparatively low and, as a result, the rate of combustion within the combustion chamber is also relatively low. Accordingly, the air flow desirably is limited during low power operation in order to enrich the air-fuel mixture in the combustion chamber primary zone.
Under high power, (also know as full power) operating conditions, the air-fuel mixture is commonly relatively rich. Under these conditions, the exhaust emissions are typically high in both visible smoke and nitrogen oxides. In order to reduce these emissions, it is desirable to increase the flow of primary air into the combustion chamber to make the fuel mixture in the primary zone leaner and to decrease the dwell time of the combustion gases in the combustion chamber. Therefore, it can be appreciated that it is desirable to control the flow of the air, for example, in relation to the operational mode of the engine.
Industrial power generation gas turbines typically include a compressor for compressing air wherein the air is subsequently mixed with fuel and ignited in a combustor for generating combustion gases. The combustion gases flow to a turbine that extracts energy for driving a shaft to power the compressor and also produces output power for powering an electrical generator. In addition, the turbine is typically operated for extended periods of time at a relatively high base load for powering the generator to produce electrical power in a utility grid, for example. In such turbines, flame stability and engine operability dominate the combustor design requirements. As such, the flow rate of air affects a recirculation flow pattern in the combustion chamber (recirculation of the burned products with incoming fuel) and thereby affects the flame stability, the level of nitrous oxide emissions (NOx) and the ability to control the load in the turbine.
Accordingly, there is a need in the art for a combustor having improved flow control of air into the combustor reaction zone.
One embodiment of the present invention comprises a flow control device for a combustor in which the flow control device comprises a shroud having a first end and a second end wherein the second end is coupled to the combustor. The shroud is disposed to receive a primary fluid and disposed to direct the primary fluid into the combustor. In addition, the shroud further comprises a plurality of ports disposed therein wherein the ports are oriented to extract a portion of a flow from a flow path of the primary fluid so as to control a flow rate of the primary fluid through the shroud.